Neutron powder diffraction experiments were carried out to investigate a change in a crystal structure of La0.8Sr0.2Ga0.65Fe0.35O3 for oxygen partial pressures, P-O2, at 800 degrees C. The crystal structure was refined on the basis of the R3c syrnmetry for the P-O2 range from 10(-1) to 10(-20) atm, by the Rietveld analysis. It was found that lattice parameters, a and c, monotonically expand with decreasing P-O2, and then both expansions are rapidly suppressed below 10(-4) atm. In the meantime, IM-O and IO-O(2) also discontinuously increased with decreasing P-O2, while IO-O(1) did not change at all P-O2, where IM-O, IO-O(1) and IO-O(2) are the bond lengths within a MO6 octahedron (M = Ga0.65Fe0.35). This result indicates that the IM-O and the IO-O(2) are more important than the IO-O(1) for such a complicated lattice expansion for P-O2. (C) 2008 Elsevier B.V. All rights reserved.